This invention has for its subject a pneumatic tire wheel for vehicles comprising a pneumatic tire so mounted to a tire rim as to define a tight sealed chamber for inflating said tire, and a predetermined amount of a two-phase system in a substantially saturated vapor balance state at the temperature and inflation pressure of said tire and introduced into said tight chamber. The invention is also concerned with a method of adjusting the inflation pressure of a pneumatic tire of the kind specified above.
In the technical field of pneumatic tires for vehicles, there are two major requirements to be met. Firstly, the tire should be prevented from deflating rapidly on the occurrence of a tire blowout or puncture; secondly, the inflation pressure of pneumatic tires should be made adjustable in as automated a manner as possible even with the vehicle running.
To meet the first-noted requirement, the prior art provides pneumatic tires with inflation chambers into which substances can be introduced or released which can stop any minor leaks developed in the tire while the vehicle is running. Examples of such wheels are disclosed in U.S. Pat. Nos. 3,910,334 and 4,130,144.
However, proper performance of the measures described therein is subordinate to the tire becoming at least partly deflated, and is limited to but very small leaks.
Accordingly, such prior measures cannot perform successfully during the initial stage of the tire deflation, irrespectively of how fast the deflation rate may be, and may prove inadequate even during the final deflation stage if the leak is a serious one.
Inasmuch as, from the standpoint of safety, preventing the tire from deflating at such a fast rate as to cause sudden and uncontrollable skidding of the vehicle has priority of concern over preventing the tire from reaching a flat condition, the measures provided by the prior art cannot be regarded as fully satisfactory.
An improvement in this technology is disclosed by Italian Patent No. 1054139, filed on Jul. 30, 1973 in the name of Dunlop Ltd. This prior patent provides for the leak stopping substances to be additivated with a volatile liquid mixture susceptible to be vaporized by the heat generated within the tire as a result of its running in a deflated condition.
Such volatile liquids are effective to create within the punctured tire pressure conditions which are acceptable at least for short distance running. The effect is brought about, of course, by the leak being stopped by the leak stopping substances.
A first technical solution proposed is of introducing that mixture of liquids in a free state unrestrictedly into the tire inflation chamber. It is recognized, however, in the patent itself, that such an approach results unavoidably in the wheel balance being affected. Alternatively, it is suggested that the mixture be stored in a purposely provided means and released into the inflation chamber on the tire deflating.
Thus, having rejected the use of free liquids in the inflation chamber, also the measures suggested in that patent can only become effective after the punctured tire has become fully deflated.
The second-mentioned requirement in the foregoing is expressed by the improved performance of wheels, in terms of traction, tire wear, travel speed, and distribution of the load over a yielding roadbed, in dependence on the inflation pressure.
As is known, for instance, in driving from an asphalt course to a sandy, muddy, snow-covered, or otherwise yielding surface, it is highly recommended that the inflation pressure of the wheel tires be decreased to enhance the tire traction and bearing surface on the ground. This is a need which is felt particularly by military, agricultural, and racing vehicles, on account of such vehicles being liable to encounter frequent changes in the nature of the roadbed.
To fill this demand, the prior art proposes complex vehicle-mounted systems whereby compressed air can be supplied to the inflation chamber of each tire even while the vehicle is running. Such systems generally include compressed air ducts which extend through the wheel hubs.
Typical examples of such prior devices are described in European Patents Nos. 0071278 and 164917.
Additionally to their highly complex construction, a major drawback of such systems is that a satisfactory seal is difficult to accomplish at the rotary fits provided in the duct paths through the wheel hub.
Such drawbacks have largely frustrated even small-scale attempts to install such systems on vehicles for normal use. Further, the components of said systems considerably burden the vehicle weight and cost.